Dry skin is common among all skin types from very light-skinned individuals to, surprisingly, those individuals who have very dark skin that is often referred to as oily. The oily skin often found on darker skinned individuals (such as those having Fitzpatrick Type IV, V, and VI skin types) is generally caused by sebum, a mixture of lipids, waxes, and the debris of dead fat producing cells. While sebum was originally believed to be present for the purposes of lubricating skin, scientists have shown that that low levels of sebaceous gland activity do not correlate with dry skin. Downing D T, Stewart M E, Wertz P W, Colton S W, Abraham W, Strauss J S (March 1987). “Skin lipids: an update”. The Journal of Investigative Dermatology 88 (3 Suppl): 2s-6s. The composition of sebum is generally believed to be about 25% wax monoesters, about 41% triglycerides, about 16% free fatty acids, and about 12% squalene.
It is now known that sebum does not lubricate or moisturize skin. Rather it tends to rest superficially on the skin surface and provide a shiny, oily appearance.
Ceramides, a family of lipid molecules found in high concentration in cell membranes of keratinocytes, are one component of the sphingomyelin lipids that make up the lipid bilayers of skin. As such ceramides are known to be excellent skin moisturizers. Interestingly enough, the keratinocytes of darker, oily skinned individuals tend to secrete an abundance of sebum but exhibit a deficiency of ceramides. This in turn causes the facial skin of these individuals to exhibit a shiny, oily appearance with underlying dry skin, and a generally dull, ashy skin tone and texture. The differences in skin properties of Caucasians, Blacks, and Asians are set forth in the article by Muizzuddin, et al., Structural and Functional Differences in Barrier Properties of African American, Caucasian, and East Asian Skin, Journal of Dermatological Science, Vol. 59 (2010): 123-128. Muizzudin, et al. demonstrate that African American subjects (those having Fitzpatrick Skin Types IV-VI) tend to exhibit a greater degree of skin scaliness, believed to be due to dryness caused by reduced ceramide levels in skin. Fitzpatrick skin types may be determined as set forth in Fitzpatrick, Thomas B.: Soleil et Peau. J Med Esthet 1975; 2:33034.
Cosmetics companies have developed products to treat each one of these conditions separately. For example, there are many well known products that contain different types of skin moisturizing agents including but not limited to ceramides. They are typically sold with marketing claims that they moisturize dry skin. Other types of products are known for desquamating skin (product marketing claims may refer to this as resurfacing), which is removing dead skin cells to provide smooth, fresh skin. Other types of products are sold for the purpose of reducing the oily shine on skin either by reducing sebum produced or absorbing sebum already produced which is referred to as “mattifying”. Other products are sold with marketing claims that they improve skin luminosity or radiance. However, there are no single products that provide all the benefits of moisturization, desquamation, luminosity, and reducing the shiny appearance of oily skin by whatever mechanism (aka mattification), especially for darker skinned individuals who have oily but dry skin and are most likely to show a ceramide deficiency in the stratum corneum.